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Project description

Development of thresholds for twospotted spider mite on greenhouse grown bent cane cut roses. (00DS029)
Program UC IPM competitive research grants program
M.P. Parrella, Entomology, UC Davis
J. Lieth, Environmental Horticulture, UC Davis
Host/habitat Roses; Flowers
Pest Twospotted Spider Mite Tetranychus urticae
Discipline Entomology
Decision Support
Start year (duration)  2000 (One Year)
Objectives Determine the relationship between mite density and visible leaf injury.

Determine the relationship between mite density during flower formation and gas exchange, transpiration ad plant yield.

Determine the mite density that stimulates upward movement onto the flowers.

California growers produce 70% of all greenhouse cut roses grown in the United States. The high quality standards for this crop have traditionally meant that it is subject to 50-60 pesticide applications per year. Half of these are typically directed against the twospotted spider mite, Tetranychus urticae. Mite feeding causes leaf chlorosis, webbing, and disruption of photosynthesis and water balance in the rose plant. In addition, there are no thresholds for mites on roses, so there are no guidelines for timing sprays or releasing mite natural enemies. This project will provide growers with information that relates mite density to the occurrence of the mite damage. This knowledge will improve timing and selection of mite control strategies.

Our work to date has been a preliminary examination of the relationship between mite density and rose plant photosynthesis and water balance. Photosynthesis is a measure of plant carbon dioxide uptake, which is converted by the plant into energy for growth. Proper water balance is essential for photosynthesis as well as many other physiological functions. Our preliminary results indicate that low spider mite densities (less than 5 mites per leaf over a five day period) do not negatively affect these parameters, but high mite densities (over 20 mites per leaf over a five day period) do have a negative impact on photosynthesis and water balance.

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